What is relational?

A relation is a set of tuples (fixed length array)

  • in other words, a single row in a single database is a relation between all the values that represent that row
  • in SQL, a relation is represented by a table, with each row being a tuple
  • a tuple is described as a function, since it maps names to values.
    • ex. for row 1, name -> "Kyle"
  • each element (cell) of the tuple is termed an attribute value
    • an attribute is the combination of the column name and its type
      • ex. age int
    • an attribute value is the cross-section of an attribute and a tuple (ie. it is a single piece of data)
  • each SQL clause will transform one or several relations in order to produce new relations.
  • Data is not relational. Rather, data has relationships.
  • relational is the concept that we have a set of elements that all share the same properties (aka attribute domains)
    • ex. if we have a table foo with 2 columns: id: int and name: text, then every single record in this database will look exactly like that.

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